There have been proposed various techniques for anti-reflection to increase transmittance and contrast or to minimize undesired reflected images in a field such as an optical lens, CRT, a liquid crystal displaying device of a computer or a word processor, and the like. As technique for anti-reflection, a technique is known which adjusts a refractive index and optical thickness of a multilayer as an optical interference layer to an appropriate value and reduces light reflection at the interface between the multilayer layer and atmospheric air. Such a multilayer is ordinarily composed of a layer of TiO2, ZrO2, Ta2O5, and the like as a high refractive index layer, and a layer of SiO2, MgF2, and the like as a low refractive index layer, and these layers are layered according to a dry coating method employing vacuum processing such as a spattering method, a vacuum evaporation method or an ion plating method. However, the vacuum processing, when materials to be processed are of large size, requires a large-scale vacuum processing apparatus, which is too expensive and time-consuming for evacuation, resulting in lowering of productivity or incapability of continuous production.
As another method for preparing an anti-reflection layer, there is a method in which a metal alkoxide such as titanium alkoxide or silicon alkoxide is coated on a substrate, dried and heated to form a metal oxide layer on the substrate. However, this method requires too high temperature such as 300° C. as the heating temperature, and may result in damage of the substrate. In contrast, the method employing a relatively low temperature such as 100° C. as the heating temperature, which is disclosed in, for example, Japanese Patent O.P.I. Publication No. 8-75904, is time-consuming for the layer preparation. Both methods have problem.
In order to solve the above problem regarding preparation time and temperature, there is a proposal described in Japanese Patent O.P.I. Publication No. 9-21902, in which an alkoxide of Ti, Zr, Ta, or In and a compound having two or more acryloyl, methacryloyl, allyl or vinyl groups in the molecule are used in combination at a low temperature to prepare a high refractive index material. There is disclosed in Japanese Patent O.P.I. Publication No. 7-209503 an optical film coating composition comprising as a main component a copolymer of an organosilicon compound having both a polymerizable group such as vinyl group, an allyl group, an acryloyl group or a methacryloyl group and a hydrolyzable group such as an alkoxy group, with a polymerizable, unsaturated monomer, which provides a layer with a binder resin component and an inorganic component uniformly mixed in a molecular level. There is further the description in this reference that the composition as described above is coated and polymerized by being heated at 100° C. for a long time or irradiated with ionizing radiation to form a film.
Further, there is a technique disclosed in Japanese Patent O.P.I. Publication Nos. 8-295846 and 9-220791, in which a composition comprising active organometallic compounds and metal oxides or silane compounds is hardened by heat or ionizing radiation to prepare an anti-reflection layer. Further, there is another technique disclosed in Japanese Patent O.P.I. Publication Nos. 5-270864, 5-279598, 6-11602, 8-122501, 8-297201, 9-21902 and 9-25350, in which a composition comprising no active organometallic compounds is hardened employing electron beam or ultraviolet ray as ionizing radiation ray to prepare an anti-reflection layer. However, there are the problems in these techniques that a part of the organic components remains unreacted, and the remained unreacted components vary with time. Therefore, the resulting anti-reflection layer causes change in the refractive index, and gradually loses an anti-reflection property.
As a method for solving the problems as described above, in that use of a vacuum apparatus results in lowering of productivity or an organic substance remains in the method in which a coated metal oxide is hardened by application of energy, there is a method as proposed in Japanese Patent O.P.I. Publication Nos. 11-133205, 2000-185362, 11-61406, 2000-147209, and 2000-121804, in which a film having an antireflection property is formed by plasma discharge processing under atmospheric pressure or under approximately atmospheric pressure.
However, although an anti-reflection film can be formed in only a small area according to the method proposed above, it is difficult to form a uniform anti-reflection film on a wide and long substrate, and it is extremely difficult to continuously form an anti-reflection film with a constant refractive index and a constant optical layer thickness.